1. Field of the Invention
The present invention relates to the collection of and sampling of assayable agents in a dielectric medium. This includes, but is not limited to, sampling air for agents whose presence or absence is determinable by bio-specific assays. The field includes sampling of air for biological agents, direction to, and deposition on, a collection means for an assay device. The agent-specific assays may include immunoassays, nucleic acid hybridization assays, or any other assays entailing ligand—antiligand interactions. Assays may include, but are not limited to, detection means which are colorometric, fluorescent, turbidimetric, electrochemical or voltammetric. Agents assayed include, but are not limited to, bio-warfare agents, pathogens, allergens or pollutants. Pathogens include screening for infectious airborne agents such as anthrax or tuberculosis organisms. Further dielectric media may include sampling of dielectric fluid medium such as oil for the food industry, or petrochemical and industrial oil.
2. Description of the Prior Art
In the prior art, there exist many examples of collection of agents from the air for bioassay. For example, the following publications describe various methods of allergen, pathogen and toxin collection for assay:
Yao et al (2009) in Aerosol Science volume 40, pages 492-502
Noss et al (2008) in Applied and Environmental Microbiology, volume 74, pages 5621-5627
King et al (2007) in Journal of Allergy and Clinical Immunology, volume 120, pages 1126-31
Earle et al (2007) in Journal of Allergy and Clinical Immunology, volume 119, pages 428-433
Peters et al (2007) in Journal of Urban Health: Bulletin of the New York Academy of Medicine, volume 84, pages 185-197
Yao and Mainelis (2006) in Journal of Aerosol Science, volume 37, pages 513-527
Platts-Mills et al (2005) in Journal of Allergy and Clinical Immunology, volume 116, pages 384-389
Sercombe et al (2004) in Allergy, volume 60, pages 515-520
Custis et al (2003) in Clinical and Experimental Allergy, volume 33, pages 986-991
Polzius et al (2002) in Allergy, volume 57, pages 143-145
Tsay et al (2002) in Clinical and Experimental Allergy, volume 32, pages 1596-1601.
Parvaneh et al (2000) in Allergy, volume 55, pages 1148-1154
McNerney et al (2010) in BMC Infectious Diseases, volume 10, pages 161-166 and device in U.S. Pat. No. 7,384,793
Other known methods of sample collection include trapping of volatile organic compounds (VOC) on activated carbon, de-sorption and analysis by mass spectrometry. See Phillips et al (2010) in Tuberculosis, volume 90, pages 145-151 and references therein. VOC's are not considered encompassed by the present invention since the assays are strictly chemical in nature, and are not bio-specific as defined here. By bio-specific is meant assays wherein the result is determined by a biological specificity such as nucleic acid specificity, antibody specificity, receptor-ligand specificity and the like. While diagnostic specificity may be achieved by VOC analysis, this is inferred by presence and amount of groups of defined organic compounds.
The foregoing prior art publications describe “dry” methods using pumping and filtration, wiping, passive deposition, electrokinetic transport etc; usually followed by an extraction step and application of the extract to an assay.
Methods for collection in a liquid stream have been described in the patent literature:
Yuan and Lin in US Patent Application 2008/0047429A1
Saski et al in U.S. Pat. No. 6,484,594 issued in 2002.
While efficiently collecting agents from the air, such liquid streaming systems inevitably result in high dilution of the sample. There is a consequent trade-off in sensitivity unless the agents are re-concentrated.
Northrup et al in U.S. Pat. Nos. 7,705,739 and 7,633,606 describe an autonomously running system for air sampling and determination of airborne substances therein. They do not specify the exact method of air sampling, nor detail how it is transferred to an assay system.
There exist numerous commercially available systems for air purification based on filtration or electrostatic precipitation. For a general description see the Environmental Protection Agency article “Guide to Air Cleaners in the Home”, U.S. EPA/OAR/ORIA/Indoor Environments Division (MC-6609J) EPA 402-F-08-004, May 2008. Numerous commercial examples of systems exist using either High Efficiency Particulate Air (HEPA) filters or electrostatic precipitation filters. Such systems are widely used for removal of particulate matter or allergens from air, including as part of domestic heating, ventilation and air conditioning (HVAC) systems. HEPA filters have the advantage of removal of particles down to the micron size range, whereas electrostatic precipitation methods have the advantage of entailing high volume flow with little or no pressure differential. See US patent by Bourgeois, U.S. Pat. No. 3,191,362 as a detailed example for the technical specification of an electrostatic precipitation system. While efficiently removing agents from the air, such air purification systems do not lend themselves to collection of samples for analysis.
Electrokinetic-based air cleaning systems have been developed and formerly commercialized by the company Sharper Image (but now discontinued) under the trade name Ionic Breeze. The original electrokinetic principle was enunciated by Brown in U.S. Pat. No. 2,949,550. This was further improved by Lee in U.S. Pat. No. 4,789,801 for improving airflow and minimizing ozone generation. Further improvements for the commercially available system are described in US patents by Taylor and Lee, U.S. Pat. No. 6,958,134; Reeves et al, U.S. Pat. No. 7,056,370; Botvinnik, U.S. Pat. No. 7,077,890; Lau et al, U.S. Pat. No. 7,097,695; Taylor et al, U.S. Pat. No. 7,311,762. In the foregoing descriptions of devices using electrokinetic propulsion, a common element is a high voltage electrode consisting of a wire. A very steep voltage gradient is generated orthogonally to the wire because of the very small cross-sectional area of the wire. The high voltage gradient causes the creation of a plasma consisting of charged particles, and kinetic energy is imparted to the charged particles by the high voltage gradient. The resulting net air flow is created by exchange of kinetic energy between charged and uncharged particles, and the net air flow is directed by the juxtaposition of planar electrodes which are at zero or opposite sign voltage to that of the wire electrode. Charged particles are electrostatically precipitated on to the planar electrodes, which may periodically be removed for cleaning. This body of work is directed toward air purification, not sample collection. However, as first described by Custis et al (2003), the Ionic Breeze device has been adapted for sample collection for allergen analysis by wiping down the electrodes with a paper tissue. The allergens were extracted from the tissue and subject to an immuno-assay. The Ionic Breeze was also used in the works of Peters et al (2007) and Platts-Mills et al (2005) for allergen collection for immunoassay analysis. Earlier, Parvaneh et al (2000) described an ionizer device with a “metal cup having a conductive surface as a collector plate”, from which allergens are extracted for assay. It is not evident how the sample is collected on the inside of a metal cup and does not adhere to the entire surface. The device was made by Airpoint AB, Stockholm, Sweden. However, there is no public information concerning the manufacture or sale of such a product by Airpoint AB, there is insufficient information for one skilled in the art to be able to understand the details of the device, and no similar device was used by the same authors in subsequent publications on environmental allergen detection. There is no mention of focusing of the sample into a potential well created by a voltage gradient.
Yao et al (2009) and Yao and Mainelis (2006) have described methods for collection of bio-assayable agents on to an assay means or device. Yao and Manielis (2006) describe blocks of agar gel in electrical contact with planar electrodes, and Yao et al (2009) describe a microtiter plate interposed between planar electrodes. Both of these works describe a flow of air driven by a pump, and electrostatically precipitating the agents to be analyzed on to the assay means. The electrodes and the agar blocks have substantially the same area in these works.
McNerney et al (2010) describe a breathalyzer device, where the individual breathes or coughs into a breathing tube, the sample collects on the internal surface of a tube, is scraped with a plunger on to an optical biosensor, an immunological binding reaction is performed and the biosensor utilizes an evanescent wave illumination system to determine the presence or absence of M. tuberculosis by scattered light.
None of the above methods consider the use of an electric field gradient forming a potential well to focus the agents on to a collection means for an assay device.